Structure and electronic properties of bilayers of boron-graphdiyne

Abstract

Boron-graphdiyne (BGDY) is a planar honeycomb structure in which boron (B) atoms placed at the corners of the hexagons are linked by butadiyne carbon chains. BGDY bilayers with different stacking have been investigated, and the most stable stacking corresponds to a structure in which one of the layers is a bit displaced along a B-B direction with respect to the other. The adhesion energies for the different stackings are rather close, suggesting that all these stackings can be experimentally accessible. The adhesion energy and the equilibrium distance between the two layers result from the balance between weakly attractive dispersion interactions and repulsive Pauli forces which arise when the atoms of the two layers come too close. The calculated electronic band structures reveal the bilayer BGDY is a semiconductor, and that some bands, those with substantial dispersion, split in two due to the layer-layer interaction. The calculated shear stress is anisotropic, and falls in the range of tens of MPa. The different stacking provides a promising way to tailor the size of the BGDY nanopores in applications of these materials as membranes for gas filtration and separation of gas mixtures.